A wind turbine comprises blades attached to a rotor hub for rotation in a rotor plane as well as a control system for pitching the blades relative to the hub. Many modern wind turbines comprise an overspeed protection system in order to protect the wind turbines against mechanical stresses at high winds, viz. at overspeed conditions. An overspeed condition occurs when the speed of a shaft of a wind turbine exceeds a specific range or threshold. During an overspeed condition, a wind turbine may experience severe mechanical stresses that may cause failure of components of the wind turbine. An overspeed protection system protects the wind turbine by initiating an emergency shutdown of the wind turbine during an overspeed event. Such an emergency shutdown may be performed by pitching of the blades of the wind turbine and/or by yawing the wind turbine out of the wind.
Requirements exist in relation to regular testing of the overspeed protection system of the wind turbine. The test is currently performed by operating the wind turbine at rotational speeds in order to observe whether the protection system operates to shut down the wind turbine at the threshold speed. This requires the wind speed to be above at least 6.5 m/s. Typically it would be advantageous if the testing of the overspeed protection system could be performed when one or more service technicians has/have other task to be performed at the wind turbine, such as servicing or maintenance.
However, the probability that the wind speed is below 6.5 m/s on a randomly chosen day is 10%, which means that in roughly 10% of the service technician visits there is not enough wind speed to test the overspeed protection system.
This necessitates extra service technician visits, which is costly and time consuming.
Hence, it would be advantageous to provide a system and a method for testing an overspeed protection system of a wind turbine which is operable independently of the present wind speed.